The present invention relates to communication interfaces for smart (IC) cards. In particular, the present invention relates to means that enable smart cards to communicate with a host through a universal serial bus (USB) connection in either full-speed or high-speed mode.
Smart cards typically communicate with a host terminal through a reader. In one type of system, the reader is also the host. In such system, the card is inserted into a slot in the reader, which brings electrical contacts in the reader into engagement with mating contacts on the exterior of the card. The engaged contacts enable a microcontroller in the reader to communicate with the memories and/or microprocessor in the smart card. Presently, most smart cards communicate with card readers in a manner compliant with the International Standards Organization/International Electrotechnical Commission (ISO) 7816. FIG. 1 is a block diagram showing the construction and connections of a stand-alone reader 10 and a smart card 12 connected according to a typical ISO-7816 connection scheme. Of the eight contact points available on a typical smart card system, the typical connection made use of five contact points: one for power supply, one for clock signal, one for data input/output, one for sending reset signals, and one for ground connection. A microprocessor 14 in the reader 10 receives clock signals from a clock 22 and inputs/output signals through the I/O line 24 and reset signal through the RST line 26.
Although the ISO-7816 is a well established and widely used standard, communication based on this standard is rather slow. Furthermore, as personal computers become ubiquitous and Universal Serial Bus (USB) connection a standard features in most PCs, smart card reader can be made cheaper by relocating the micro-processing and memory functions from the reader (the card contacting mechanism) to a separate host PC, so that the reader becomes a simple USB connector. The USB protocol is a private industry standard sponsored by USB Implementers Forum, Inc., a joint initiative of Intel, Hewlett-Packard, Lucent, NEC, Philips, Microsoft and others. The protocol works in conjunction with the IEEE 1394 standard connector.
FIG. 2 is a block diagram that shows a typical construction and connections of a smart card reading system that utilizes a computer and a USB connection. In FIG. 2, a personal computer 40 communicates with a smart card 46 via a USB cable connection 42 with a connector head 44 (the xe2x80x9ccard readerxe2x80x9d), which calls for 4 wires: one for the power Vcc, one for the ground GND, and a pair of differential data transmission wire DATA+ 50 and DATAxe2x88x92 52. A first generation USB standard (version 1.1) allows transmission in two modes: a low speed mode and a full speed mode. For low speed transmissions, such as Control Transfer and Interrupt Transfer under USB 1.1, the data is clocked within the computer 40 at 1.5 Mbps with a data signaling tolerance of xc2x1 1.5% (or 15,000 ppm). For full speed transfer such as Isochronous Transfer or Bulk Transfer under USB 1.1, the data is clocked at 12 Mbps with a data signaling tolerance of xc2x1 0.25% (or 2,500 ppm). In addition to the two modes mentioned above, a newer USB standard (version 2.0) calls for a third (high speed) transmission mode where the data signaling rate is set at 480 Mbps with a data signaling tolerance of xc2x1 500 ppm.
At any given speed of transmission, because the USB cable 42 does not have a separate wire to carry a clock signal, a clock generator has to be present at both ends of the cable 42. At the host end, most readers and computer systems have a highly accurate system clock 60 that can be use for both reception and transmission purposes. At the card end of the cable 42, a low cost electronic resonator 48 could be used for low speed transmission. Such resonators 48 are typically integrated into the smart card""s microprocessor 58, as shown in FIG. 2. However, such a low cost resonator 48 is not accurate enough to clock transmissions at either full speed or high speed. Presently, in order to have a full speed or high-speed transmission system, an accurate clock element, such as a crystal oscillator, has to be introduced into the reader/connector. FIG. 3 shows a typical high speed USB reader/connector 44 that connects a highly accurate clock element 62 to one of the contact pins 60. Earlier generations of USB smart card connectors lacking an accurate clock element (FIG. 2) would become obsolete. However, since there is still a large installed base of low speed USB smart card connectors, it would be desirable to have a smart card that can use any of these connectors in a full speed or high speed transmission mode, regardless of whether the connector 44 has or does not have a clock inside.
Since having a clock element in the reader/connector adds complexity and thus cost to the manufacturing of the reader/connector, it would also be desirable to have a smart card system that eliminate the need for a clock element in the reader/connector module.
The present invention is a smart card that has a highly accurate clock element connected to its microprocessor. The incorporation of an accurate clock element enables the smart card to be used with any USB enabled smart card readers/connectors for either full speed or high-speed data transmission. The accurate clock element can be a clock ceramic oscillator, a resonator, or any vibrating device, provided that it has an accuracy sufficient to achieve at least full speed, and preferably also high speed, data transfer (e.g., an accuracy of at least 0.25%) and a thickness meeting standards for placement on smart cards (e.g., preferably not more than 0.6 mm).